1. Field of the Invention
This invention relates to an automatic reset circuit, especially to a reset circuit with transient detection function for detecting transient variations of the supply voltage (VDD) and the electric ground (GND) of an electric system.
2. Description of Related Art
Today, electric systems are greatly used in our daily life such as in televisions, computers, receivers, air conditioners, and mobile phones. Noise and disturbance are thus introduced in our environment, and they can heavily damage the inner circuits and normal functions of electric systems. Rippled supply voltages (VDD) of power sources and the voltage-level bias of an electric ground (GND) are very common and dangerous events in electric systems. These events always cause electric systems to experience improper operations, devices or circuit break, and system halt. Hence, it is the major objective of reset circuits in electric systems to protect their inner circuits and survive their normal operations. A commonly used reset circuit of the prior art is a manual reset device such as an electric switch., but it is manually enabled by experienced users. FIG. 1 is an automatic reset circuit of the prior art, which is commonly used in many integrated circuits. The automatic reset circuit includes a detecting unit 14, a resistor 12, a capacitor 13, and a trigger circuit 15 connected to the detecting unit 14. One end of the resistor 12 is connected to a supply voltage port 10 of a power source, and the other end of the resistor 12 is linked with one end of the capacitor 13 and the input port 141 of the detecting unit 14 to form a note 16. The other end of the capacitor 13 is joined with an electric ground 11. If the voltage variation between the supply voltage port 10 of the power source and the electric ground 11 exceeds the threshold of the detecting unit 14, the trigger circuit 15 is enabled. The automatic reset circuit of an electric system of the prior art usually detects the DC-level or low-frequency voltage variations in of the power source to reset the electric system automatically when the power source is turned on. In general, the rise time of the automatic reset circuit of the prior art is not faster than one microsecond (.mu.s). However, the automatic reset circuit of the prior art is not sufficient to detect a nanosecond transient voltage variation in the system-level electrostatic discharge (ESD) test of an circuit board, the electrical fast transient/burst (EFT) test of a power line, and the automatic resetting and voltage compensating objectives of an complex electric system such as a VLSI system. A new automatic reset circuit is indeed required to detect much faster transient voltage variation of an electric system.